If thinset will stick to it, I'd take panels of Kerdiboard, put some significant piles of thinset on it, then like you might spot a tile on a wall, treat the Kerdiboard panel like a huge tile to get the wall perfectly flat, plumb, and ready for tiling. You'll need a long level to ensure you don't warp the panel when 'setting' it to the wall as you press it into the piles of thinset. They have a video on the Schluter YouTube account showing just this to ready a tiled wall over an uneven cement wall. If thinset won't stick reliably...I'd have to think about it. Since they often put stucco over adobe (if I remember correctly), thinset should work.